Gene expression signatures of site-specificity in cancer metastases

We have previously shown that metastases are generally characterized by a core program of gene expression that induces the oxidative energy metabolism, activates vascularization/tissue remodeling, silences extracellular matrix interactions, and alters ion homeostasis. This core program distinguishes metastases from their originating primary tumors as well as from their target host tissues. We hypothesized that organ preference is reflected in additional, site-selective components within the metastatic gene expression programs. Expanding our prior analysis of 653 human gene expression profiles plus data from a murine model, we find that the release from the primary tumor is associated with a suppression of functions that are important for the identity of the organ of origin, such as a down-regulation of steroid hormone responsiveness in the disseminated foci derived from prostate cancer. Metastases adjust to their target microenvironment by up-regulating—even overexpressing—genes and genetic programs that are characteristic of that organ. Finally, alterations in RNA and protein processing as well as immune deviation are common. In the clinic, metastases are mostly treated with the chemotherapy protocols devised for their primary tumors. Adjustments that account for the gene expression differences between primary and metastatic cancers have the potential to improve the currently dismal success rates.